The invention relates to a method for balancing a cylinder, roll or equivalent part with a thin mantle intended to be revolving. The deformations of said part while the part revolves are controlled by this method.
The invention also relates to a balanced cylinder, roll or equivalent part having a thin mantle which is intended to be revolving.
In the state of the art, it has been observed that the round shape of a drying cylinder becomes oval when the cylinder is rotated. The effect of this deformation cannot be eliminated by means of the modes of balancing known from prior art because it causes dynamic run-out, which is due to deviations in the circumferential deflection line. By means of prior-art balancing methods it has not been possible to control the problems caused by the states of dynamic run-out because the known methods compensate for deviations in the axial deflection line. In some instances, such deviations in the circumferential deflection line cause many problems, for example, inaccuracy in doctoring, wear of a doctor blade, fluttering of a web, and an increase in the curvature of the seam of a wire. Moreover, it has been necessary to use a thicker mantle than required by other dimensioning considerations in order that the problems associated with the dynamic run-out might be solved.
The above-noted prior-art problems associated with dynamic run-out will be further aggravated in the future when the running speeds of paper machines increase.
With regard to the prior art, reference may be made to FI Patent 82856, which discloses a method for balancing a roll in which an annular rail is fixed to the inner face of the roll and a balance weight is attached to said rail. The rail is fixed to the inner part of the roll mantle only at the ends of the rail and preferably close to the longitudinal joint of the tubular roll. The final fixing of the rail takes place at the stage at which the longitudinal jointing of the tubular roll is performed. This known method rectifies an error in the axial deflection line of the roll, but it cannot rectify deviations in the circumferential deflection line occurring in a cylinder, roll, or equivalent part with a thin mantle during rotation, when the mantle changes its shape, for example, flattens. Thus, by this arrangement it is not possible to rectify the uneven mass distributions resulting, for example, from differences in the thickness of the mantle.
An object of the invention is to provide a method for balancing a cylinder, roll or equivalent part having a thin mantle, by which method the deviations in the circumferential deflection line of the mantle can be compensated for such that the states of dynamic run-out do not cause problems when a cylinder, roll, or equivalent part with a thin mantle revolves.
An object of the invention is thus to provide a method which compensates for the deviations in the circumferential deflection line, which deviations depend on differences in the thickness/mass of the mantle and thus produce deformations and unbalance when a cylinder, roll or equivalent part with a thin mantle revolves.
With a view to achieving the above objectives and those that will come out later, the method in accordance with the invention is mainly characterized in that the method comprises the following steps:
In the method, the deviations in the circumferential deflection line of a mantle of a cylinder, roll or equivalent part with a thin mantle are measured, and dynamic unbalance is determined,
locations and magnitudes of counterweights necessary for balancing are determined based on the deformations and dynamic run-out arising from the deviations in the deflection line of the mantle, and
the counterweights are fixed to the inner face of the mantle of the cylinder, roll, or equivalent part with a thin mantle in order to compensate for the deviations in the circumferential deflection line and, thus, to eliminate the dynamic run-out.
The cylinder, roll or equivalent part with a thin mantle in accordance with the invention is, in turn, characterized in that counterweights of magnitudes necessary for balancing are fitted to the inner face of the mantle of the cylinder, roll or equivalent part with a thin mantle, to positions determined on the basis of measurements, in order to compensate for the deviations in the circumferential deflection line of the mantle such that, when the cylinder, roll or equivalent part revolves, the circumferential deflection line is compensated for and dynamic run-out is eliminated.
In the method in accordance with the invention, the deviations in the circumferential deflection line are compensated for such that the dynamic run-out is determined first by measurement and the need for balancing is determined by calculation, and the cylinder is balanced by fitting counterweights to the inner face of the mantle, the magnitude and position of said counterweights being thus determined by calculation on the basis of unbalance measurements. The measurements may be performed by a balance machine and/or as ultrasound measurement and/or as manual measurement so as to find out the differences in the thickness/mass of the mantle causing deviations in the circumferential deflection line, which differences are compensated for by means of counterweights fitted to the inner face of the roll, which counterweights rectify the deformation of the mantle such that, when the cylinder, roll, or equivalent part having a thin mantle revolves, its shape does not change, and the rotation thus takes place in a state of balance.
In accordance with the invention, some counterweights, which are preferably longitudinal, are fitted inside a drying cylinder mainly in the middle area of the mantle in the longitudinal direction in order to cancel the deformation of the mantle. The counterweights are fitted to positions determined by calculation, and if a cylinder mantle is involved that becomes, for example, oval during rotation, the counterweights are fitted preferably on two sides of the mantle such that they are situated at both ends of the minor axis of an ellipse, that is, at the narrowing of the diameter. The counterweights may be fixed, for example, inside heating strips made of a U-channel and nowadays placed on the inner face of a cylinder, to the portions between arc hoops. When rolls are balanced in a similar way, the weights may be fixed either by means of screw couplings to the inner face of the mantle or, for example, by means of arc hoops. The counterweights may, of course, be also attached in many other ways familiar in itself to a person skilled in the art; in cylinders, however, special attention shall be paid to the fact that the mantle of the cylinder must not be damaged.
In the arrangement in accordance with the invention, advantages are achieved when the dynamic run-out decreases, in which connection, among other things, savings in costs are achieved since the thickness of the mantle can be reduced because of the decrease in unbalance. Moreover, it is possible to xe2x80x9csavexe2x80x9d cylinders, rolls or equivalent whose unbalance would otherwise exceed the limit of rejection. In addition, doctoring is improved because the shape remains round with the result that the blade pressure of the doctor is constant for a revolution of a cylinder, whereby the life of doctor blades also increases. Furthermore, fluttering of the web decreases and the curvature of the seam of the wire is reduced and the need for after-balancing also diminishes when rotation takes place without any unbalance. Moreover, the arrangement in accordance with the invention reduces the need for precision machining because the mass/thickness deviations and/or machining deviations of material can be compensated for by the method in accordance with the invention.
When the method in accordance with the invention is compared with prior-art methods, one essential difference is that the prior-art methods compensate for an error in the axial deflection line, whereas the method in accordance with the invention compensates for deviations in the circumferential deflection line, which deviations depend on differences in the thickness/mass of the mantle.